Collagen is a fibrous protein that is composed of a triple chain helix structure having a sequence of repeating amino acids, glycine, and X and Y, X and Y being any amino acid, but are usually proline and hydroxyproline. The X and Y amino acids, particularly proline, in addition to the presence of imino acid residues, stabilize the helical structure of collagen.
Collagen constitutes one quarter of the total amount of protein in the human body. It is the major fibrous element of skin, bone, tendons, cartilage, ligaments and blood vessels. Collagen represents about 70% of skin in terms of its dry weight and helps form the structural network of skin. The presence of collagen provides strength and resiliency in skin. While there are various types of collagen throughout the body, the collagen in skin is predominantly Type I and Type III, where 80% to 90% is Type I and the remaining 10% to 15% is Type III. Other types of collagen in skin, for example, Type IV, V, and I trimer are present in considerably smaller amounts.
Collagen is synthesized by fibroblasts. It is believed that as skin ages, the dermis and the epidermis thin because fibroblasts lose their ability to react to growth factors for the proliferation and synthesis of collagen. It has also long been recognized that there is a cause-and-effect relationship between prolonged and/or repeated exposure to UV light and the premature aging of skin. Excessive exposure to the sun contributes substantially to premature reduction in the quality and quantity of collagen in skin. These changes manifest themselves externally by typical signs of aging, such as deep lines and wrinkles, loss of elasticity, skin dryness and unevenness, and increased frequency of blotches, pigmented spots, and benign as well as malignant neoplasms. Kucharz, E. J., "The Collagens: Biochemistry and Pathophysiology", (Springer-Verlag Berlin Heidelberg 1992), pps. 6-29, 79-80, 227-232.
To counteract the undesired effects of both types of aging (i.e., natural and photo-induced), methods of increasing collagen synthesis have been investigated using, for example, a retinoic acid, aminoethyl compound, certain types of growth factors, ginsenoside, ascorbic acid, or tocopherol. See, for example, Kim et al., The Journal of Investigative Dermatology, 98:359-363 (1992); Griffiths, C. E. M. et al., The New England Journal of Medicine, 329: 530-535 (1993); Chojkier et al., The Journal of Biological Chemistry, 264(28):16957-16962 (1989); U.S. Pat. Nos. 5,747,538, 5,747,049 and 5,386,012. In addition, there has been research involving the stimulation of collagen with a peptide. The peptide, in the form of a hydrolysate obtained by fermentation of milk proteins, was found to increase the thickness of the stratum corneum. It did not, however, significantly increase the level of collagen. Augustin et al., Skin Pharmacol 10: 63-70 (1997).
Thus, while various species are known to stimulate collagen synthesis, the topical compositions of the present invention provide a synergistic combination that unexpectedly enhances the stimulation of collagen synthesis. As there is a continued desire to maintain the health of the skin for the purpose of appearing attractive and prolonging a youthful look, a boost in the production of collagen in the skin is important and is the object of the present invention.